Techniques for displaying simulated airport visual approach glideslope indicators on aircraft cockpit displays are known. An example of such a technique is disclosed in commonly assigned U.S. Patent Application Publication No. US 2002/0099528 A1 to Charles L. Hett (“Hett”), which is incorporated herein by reference in its entirety. As described in Hett, aircraft landing at airports during marginal Visual Meteorological Conditions (VMC) or in situations where there are reduced visual cues (e.g., night flights) are aided by an Instrument Landing System (ILS). An ILS provides a radio beam that originates on the ground at an ILS-equipped airport and generates a glideslope that an aircraft can follow during an instrument approach to the runway. The ILS radio beam is detected by equipment onboard the aircraft and provides lateral, along-course, and vertical guidance to aircraft attempting to land at that airport. However, some airports do not have an ILS-generated radio glideslope.
Nevertheless, airports may substitute for an ILS and/or provide airport lighting aids in addition to the ILS, as described in the U.S. Federal Aviation Administration's (FAA's) publication entitled “Aeronautical Lighting and Other Airport Visual Aids.” The airport lighting aids may provide vertical visual approach slope guidance to the runway, which is especially useful during marginal VMC or in situations where there are reduced visual cues. For example, various existing Approach Lighting Systems (ALSs) provide techniques that can be used by flight crews to transition from instrument flight to visual flight in order to land. An ALS provides a directional pattern of high intensity signal lights that start at a landing threshold of the runway, and extend a prescribed distance into the approach area. The signal lights shine upwardly toward the aircraft along the approach slope or glide path and visually guide the pilot during the approach and landing. Some ALSs include sequenced flashing lights which appear to the pilot as a ball of light traveling towards the runway at high speed.
A well known airport lighting aid is the Precision Approach Path Indicator (PAPI) system. The PAPI system uses a single row of either two or four light units, which have a visual range of about 5 miles during the day and up to 20 miles at night. Typically, the row of light units is installed on the left side of the runway. The two or four identical light units are arranged on the side of the runway in a line perpendicular to the runway centerline to define the visual glide path angle. Each light unit has a white segment in an upper part of the beam and a red segment in a lower part of the beam, with the segments separated by a pink transition zone. In a two-light PAPI system, the lights are positioned and aimed to produce a signal presentation wherein a pilot, in an aircraft which is on or close to the established approach path, sees the light unit nearest the runway as red and the second light unit as white. If the aircraft is above the approach path, the pilot sees both light units as white. If the aircraft is below the approach path, the pilot sees both light units as red.
In a four-light PAPI system, the signal presentation is such that a pilot, in an aircraft which is on or close to the established approach path, sees the two light units nearest the runway as red, and the two light units farthest from the runway as white. If the aircraft is above the approach path, the pilot sees the light unit nearest the runway as red, and the three light units farthest from the runway as white. If the aircraft is further above the approach path, the pilot sees all of the light units as white. If the aircraft is below the approach path, the pilot sees the three light units nearest the runway as red, and the light unit farthest from the runway as white. If the aircraft is further below the approach path, the pilot sees all of the light units as red.
The Visual Approach Slope Indicator (VASI) system is another well known airport lighting aid system. The VASI system provides a visual glide path angle by directing a beam of light at approaching aircraft to indicate to the pilot whether the aircraft is within the appropriate glide path for approaching the intended runway. VASI systems are visible at a range of about 3–5 miles during the day, and up to 20 miles or more at night. However, VASI systems are typically arranged to provide visual descent guidance information during the approach but after the aircraft is visually aligned with the runway. Lateral course guidance is provided independently by the runway or runway lights.
VASI system installations are typically 2, 4, 6, 12 or 16 light units arranged in parallel to the runway centerline or as bars (commonly referred to as near, middle and far bars). Typical VASI installations can be 2 bars, near and far, and may include 2, 4 or 12 light units. Two-bar VASI installations provide one visual glide path which is normally set at 3 degrees. Some VASI installations are three bars spaced intermittently along one or both sides of the runway, near, middle and far, to provide an additional visual glide path to accommodate high cockpit aircraft. Three-bar VASI installations provide two visual glide paths. The lower glide path is provided by the near and middle bars and is typically set at 3 degrees, while the upper glide path, which is provided by the middle and far bars, is typically ¼ degree higher. This higher glide path is intended for use only by high cockpit aircraft to provide a sufficient Threshold Crossing Height (TCH). VASI installations having 2, 4 or 6 light units are located on one side of the runway (typically the left side). If a VASI installation includes 12 or 16 light units, they can be located on both sides of the runway.
The basic principle of the VASI system is that the colors are differentiated between red and white. Each light unit aims a narrow split beam of light at approaching aircraft. Each light has a white segment in the upper part of the beam and a red segment in the lower part of the beam, and the transition zone between segments is pink. The light units are arranged so that a pilot using the VASI system during an approach sees the combination of lights for a 2-bar VASI (4 light unit) system. For example, the farthest light unit of a two-unit system is aligned and positioned so that the bottom of the red or lower segment is parallel to the glide path and forms the upper limit of an ideal glide path for the runway. In such a system, the light unit closest to approaching aircraft is aligned and positioned so that the top of the white or upper segment is aimed into the glide path, and the bottom of the white segment is substantially parallel to the glide path and forms the lower limit of the ideal glide path. If an aircraft is on the proper glide path, the closest light unit appears to be white to the pilot, and the farthest light unit appears to be red. If the approach is too high, both light units appear to be white. If the approach is too low, both light units appear to be red.
Another known airport lighting aid system uses a tri-color lighting technique. Typically, tri-color visual approach slope indicators are arranged as a single light unit that projects a three-color visual approach path into the final approach area of the runway. The below glide path indication is red, the above glide path indication is amber, and the on glide path indication is green. Tri-color visual approach slope indicators have a visual range of approximately one-half mile to one mile during the day, and up to five miles at night.
A fourth known airport lighting aid system uses a pulsating light. The visual approach slope indicators are arranged as a single light unit that projects a two-color visual approach path into the final approach area of the runway. The on glide path indication is a steady white light. The slightly below glide path indication is a steady red light. If the aircraft descends further below the glide path, the red light starts to pulsate. The above glide path indication is a pulsating white light. The pulsating rate increases as the aircraft deviates further above or below the desired glide path. The visual range of the pulsating light system is about 4 miles during the day, and up to 10 miles at night.
However, a significant problem with the existing airport lighting aids, such as the PAPI, VASI and other visual approach indicators, is that although the approach lighting systems at an airport can be visible at a range of 10 miles or more, the validity of the lighting systems (e.g., in terms of accuracy and landing safety) for visually indicating a glide path is limited to a distance which is less than 5 miles from the airport. Furthermore, the validity of the lighting systems for indicating a glide path is also dictated by the type of approach slope lighting indicator system being used (e.g., PAPI, VASI, etc.). Notably, a recent near-accident of a corporate jet near Scottsdale, Ariz. can be attributed to the flight crew's unawareness or disregard of the variable distance versus lighting system validity problems that affect the accuracy and safety of an airport's approach slope lighting indicator system. In any event, another significant problem with the existing airport lighting aids is that the compelling nature of the lights can cause flight crews to take an “on glide path” indication at face value, regardless of the aircraft's distance to the airport. Consequently, if an aircraft is more than 5 miles from an airport, an apparent (to the flight crew) visual indication that the aircraft is on the glide path is likely incorrect (with significant potential airport and landing safety consequences). Therefore, it would be advantageous to have a system and method for displaying the validity of airport visual approach slope indicators on an aircraft display. As described in detail below, the present invention provides such a system and method, with an aircraft display that indicates the validity of airport visual approach slope indicators.